JPH1163941A - Depth measurement of ferrite decarburized layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can measure the depth of a ferrite decarburized layer automatically and exactly by using an image processing method. SOLUTION: After the cross-section image of an object to be inspected is shot and image-divided (S1) and shading correction is conducted (S2), binary processing is conducted (S3). A plurality of long divisions to be processed are set in the direction parallel to the surface of the object to be inspected (S4), and the number of white picture elements in the respective divisions to be processed is counted in order from the surface side (S5). It is discriminated whether or not the number of white picture elements is a prescribed value or lower (S6). If it is a prescribed value or lower, a distance to the division to be processed is discriminated as a ferrite decarburized layer depth (S7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the depth of a ferrite decarburized layer appearing on a surface of a steel material or the like.

[0002]

2. Description of the Related Art Steel materials (steel materials) including special steels used for members of automobiles and industrial machines, etc., are exposed to oxygen in the atmosphere during the manufacturing process such as rolling and heat treatment. The oxygen inside reacts and dissipates from the steel as CO and CO ₂ . Therefore, the carbon content on the surface and near the surface of the steel material is different from the carbon content inside the steel material.
This is called decarburization, and the portion where carbon is reduced is called a decarburized layer. Since the decarburized layer has low strength, when steel is processed into a product, there is a possibility of causing a problem of insufficient strength. In particular, a ferrite decarburized layer consisting of only ferrite exists near the surface of the steel material, which causes a problem in strength.

[0003] Therefore, when a product is shipped from a steel maker to a user, it is necessary to inspect the depth of the decarburized layer of the ferrite after predetermined treatment and to assure that the depth is within an acceptable range.

As an inspection of the depth of the decarburized layer of ferrite, a sample in which a part of a steel material is cut out and the periphery thereof is solidified with a resin is produced, and a cut surface of the sample is enlarged and inspected by a microscope or the like. . When corroded using a corrosive liquid and inspected under a microscope, a method of taking a photograph and examining the depth of a steel material sample has also been carried out because the portion of only ferrite has a color difference as compared with other portions.

[0005]

As described above, since the measurement of the depth of the decarburized layer of ferrite has been carried out by visual observation, there is a problem that there is variation between persons and that inspection requires skill. .

The present invention has been made to solve such a problem, and provides a method for automatically and accurately measuring the depth of a decarburized ferrite layer by using an image processing technique. The purpose is to:

[0007]

The object of the present invention is to take a cross section near the surface of an object to be inspected in which a phyllite decarburized layer is present from a surface to an inner surface by an imaging means, and decompose the taken image into pixels. Binarize the value corresponding to the brightness of each pixel, and set a plurality of processing target sections that are long in the direction parallel to the surface of the inspection object in the depth direction, and correspond to the high brightness included in each processing target section. The number of pixels having a value to be processed is counted for each processing target section, and the distance between the processing target section where the counted value is equal to or less than a predetermined value and the surface of the inspection object is defined as the depth of the ferrite decarburized layer. The feature is solved by a method for measuring the depth of a ferrite decarburized layer (claim 1).

By performing such image processing, the ferrite decarburized layer can be accurately recognized, so that accurate depth measurement can be performed.

By performing shading correction prior to binarization (claim 2), it is possible to correct variations in shading due to uneven light sources and to stabilize the binarization level.

Further, among the processing target sections in which the number of pixels having a value corresponding to high brightness included in the processing target section is equal to or more than a predetermined value, the position of the processing object section closest to the surface of the inspection object is taken as the position. By determining the surface position of the inspection object (claim 3), the surface position of the inspection object can be accurately determined.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of an apparatus used for implementing the present invention. In microscope 1,
An imaging lens is attached to the eyepiece section, and an imaging device 16 for taking an image of the surface to be inspected through the imaging lens is attached to the upper portion. The stage 17 on which the object to be inspected is placed can be moved in the front-rear and left-right directions by driving a pulse motor provided in the plane driving mechanism 18 by a signal from the auto stage driver 10. In addition, the vertical movement mechanism 19 is operated by the auto focus driver 11 to move the stage 17 in the up-down direction to focus.

The A / D converter 2 converts a video signal from the imaging device 16 into a digital signal, and an input buffer temporarily stores the data. The bus 4 transmits signals, the program memory 5 stores a program that defines the operation of the apparatus, and the CPU 6 controls the entire apparatus by using the program.

The image processor 7 performs grayscale image processing, binarization processing, image analysis, and the like of input image data. The gray image memory 8 stores gray image data with gradation, and the binarized image memory 9 stores binarized data.

The auto stage driver 10 includes a CPU 6
By controlling the plane moving mechanism 18 in accordance with the instruction from, the stage 17 on which the object to be inspected is placed is moved in the front-rear and left-right directions to set the position and area of the object to be inspected. The auto focus driver 11 controls the vertical movement mechanism 19 according to an instruction from the CPU 6 to automatically focus.

The output buffer 12 temporarily stores the data to be output, and the D / A converter 13 converts the data into a video signal and displays it on the CRT 14. Keyboard 15, mouse 1
5 'allows the operator to input instructions and data.

FIG. 2 is a flowchart showing an example of the embodiment of the present invention. In FIG. 2, blocks enclosed by solid lines correspond to claim 1, and blocks enclosed by broken lines are added in claim 2, and are implemented as necessary.

First, in step S1, an image of a cross section near the surface of an object to be inspected is taken using the apparatus shown in FIG. 1, and the image screen is divided into 512 × 512 pixels.
Then, the brightness is stored in the grayscale image memory 8 as a grayscale image of 8 bits, that is, 256 levels.

Next, shading correction is performed in step S2. Shading correction is widely performed in order to remove shading noise of an image due to uneven illumination or the like, and a known one can be selected and used. After performing the maximization process on the wide neighborhood, the image subjected to the similar minimization process is subtracted from the original image to obtain an image with fine irregularities, and a density bias close to the average value is added to this image doing. As a result, a gentle and uneven background due to uneven illumination or the like is corrected.

As the maximization processing of a wide range, 41 ×
It is preferable to use 41 operators. 3 × 3 operator (8 neighborhood operators) instead of 41 × 41 operator
Is repeated 20 times to obtain a similar effect in a short time. Similarly, in the minimization processing, the 8-neighbor operator processing is repeated 20 times.

In the case of 3 × 3, that is, an example of an 8-neighbor operator, among the 512 × 512 pixels, the gradation of the pixel present in the i-th row and the j-th column is represented by x _ij , and the processed i-th row and the j-th column are represented by x _ij Assuming that the gray level of an existing pixel is x ′ _ij , x ′ _ij = MAXx _mn
(I-1≤m≤i + 1, i-1≤n≤i + 1). Minimization process, 'When _ij, x' the gradation of the pixels existing in row i and column j shown in x _ij, the gradation of the pixels existing in row i and column j of the processed x _ij = MINx _mn ( i-1
≦ m ≦ i + 1, i−1 ≦ n ≦ i + 1).

The shading correction is not limited to the above method. The output of the low-pass filter may be subtracted from the original image, or the output of the wide-range average filter may be subtracted from the original image.

Subsequently, in step S3, the value for the brightness of each pixel is binarized. The threshold value for binarization is determined by, for example, employing an average value of a portion which is clearly a decarburized layer and a portion which is not. Hereinafter, among the binarized pixels, a pixel corresponding to high brightness is referred to as a “white pixel”, and a pixel corresponding to low brightness is referred to as a “black pixel”.

Next, a processing target category is set. This state will be described with reference to FIGS. FIG. 3 is a diagram showing a cross section of a material to be inspected, pixels, and processing target divisions. In FIG. 3, reference numeral 21 denotes the surface of the object to be inspected, reference numeral 22 denotes a boundary between the ferrite decarburized layer and other portions, and the hatched portion is a portion other than the phyllite decarburized layer, and the non-hatched portion near the surface is the ferrite decarburized layer. Is shown.

A number of small squares are pixels, A1 to A8
Indicates a processing target category. That is, in FIG.
Each processing target section is composed of a set of 14 pixels in a direction parallel to the surface 21 of the inspection object and one pixel in the depth direction. Of course, the number of pixels in each direction in the processing target section can be set arbitrarily, but the processing target section needs to be lengthened in a direction parallel to the surface of the inspection object.

FIG. 4 is a diagram showing two of the processing target sections A1 to A8.
The state of the pixel after the value conversion is shown. A hatched portion indicates a black pixel, and a portion other than the hatched portion indicates a white pixel.

In step S5, the number of white pixels in the processing section is counted in order from the processing section on the side closer to the surface of the inspection object. Then, step S6
In, it is determined whether or not the number of white pixels is equal to or less than 95% of the total number of pixels in the processing target section, for example.

If the number of white pixels is equal to or less than 95% of the total number of pixels, the process proceeds to step S7, where the processing target section is determined to be the end of the phyllite decarburized layer, and the processing target division is determined from the surface. The distance to the section is determined as the ferrite decarburized layer depth, and the processing is terminated. The number of white pixels is 9 of the total number of pixels
If the number does not fall below the number corresponding to 5%, the process returns to step 5 and the number of white pixels for the next (farther side from the surface) processing section is counted.

In the case of FIG. 4, the number of white pixels is equal to or less than 95% of the total number of pixels in the processing target section A6.
The distance from the surface to the treatment target section A6 is defined as the ferrite decarburized layer depth.

On the outermost surface, the object to be inspected does not enter the pixels, and as a result, the number of black pixels may increase. As a countermeasure against such a case, a process of determining the surface of the inspection object is added. That is, it is determined that among the processing target sections, the one in which the number of white pixels exceeds a predetermined value first corresponds to the surface of the inspection object, and is set as a reference plane for measuring the depth of the ferrite decarburized layer.

[0030]

EXAMPLES The depth of the decarburized ferrite layer was measured using the method described in the embodiment of the present invention, and compared with human visual data. As a result, the number of samples is 1
0, the average error was 0.005 mm, and the standard deviation was 0.008 mm. This is a very satisfactory value as an automatic measurement result.

[0031]

As described above, according to the present invention, a cross section near the surface of an object to be inspected in which a phyllite decarburized layer is present from the surface toward the inner surface is photographed by the imaging means, and the photographed image is taken as a pixel. The values corresponding to the brightness of each pixel are binarized, and a plurality of sections to be processed that are long in a direction parallel to the surface of the object to be inspected are set in the depth direction. The number of pixels having a value corresponding to the degree is counted for each processing target section, and the depth of the ferrite decarburized layer is determined by the distance between the processing target section where the counted value is equal to or less than a predetermined value and the surface of the inspection object. Therefore, the depth of the ferrite decarburized layer can be accurately measured.

Further, shading correction can be performed prior to binarization, correction of unevenness in shading due to uneven light sources, and constant binarization level can be achieved.

Further, among the processing target sections in which the number of pixels having a value corresponding to the high brightness included in the processing target section is equal to or more than a predetermined value, the position of the one closest to the surface side of the object to be inspected is defined as By determining the surface position of the inspection target, the surface position of the inspection target can be determined accurately.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of an apparatus for implementing the present invention.

FIG. 2 is a flowchart illustrating an example of an embodiment of the present invention.

FIG. 3 is a diagram showing a cross section of a material to be inspected, pixels, and processing target divisions.

FIG. 4 is a diagram corresponding to FIG. 3, showing black and white of a pixel in a processing target section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microscope 2 A / D converter 3 Input buffer 4 Bus 5 Program memory 6 CPU 7 Image processor 8 Grayscale image memory 9 Binary image memory 10 Auto stage driver 11 Auto focus driver 12 Output buffer 13 D / A converter 14 CRT Reference Signs List 15 keyboard 15 'mouse 16 imaging device 17 stage 18 plane moving mechanism 19 vertical moving mechanism 21 surface of inspected object 22 boundary surface between ferrite decarburized layer and other parts A1 to A8 processing target category

Claims (3)

[Claims] 1. A section near the surface of an object to be inspected in which a phyllite decarburized layer exists from a surface to an inner surface is photographed by an imaging means, and the photographed image is decomposed into pixels to correspond to the brightness of each pixel. The values are binarized, and a plurality of processing target sections long in a direction parallel to the surface of the inspection object are set in the depth direction, and the number of pixels having a value corresponding to high brightness included in each processing target section is determined. The depth of the ferrite decarburized layer is characterized in that the distance between the processed section where the count value is equal to or less than a predetermined value and the surface of the inspection object is defined as the ferrite decarburized layer depth. Measuring method. 2. The method according to claim 1, wherein shading correction is performed prior to binarization. 3. Among the processing target divisions in which the number of pixels having a value corresponding to high brightness included in the processing target division is equal to or more than a predetermined value, the position of the one closest to the surface side of the inspection target is defined as 3. The method for measuring the depth of a decarburized layer of a ferrite according to claim 1, wherein the surface position of the inspection object is determined.